Since the end of Punk Hazard this thought keeps crossing my mind
every time chopper is shown: "Is he falling behind?" During
Fishman Island the reveal of his power up was interesting and
exciting and during Punk Hazard he saw more of his growth as
doctor. But after that he seems to have reached a stalemate while
the rest of the crew are still showing new stuff:

Luffy showed his Gear Fourth and expected to show more
forms.

Zoro his Busoushoku Kouka.

Nami has shown to skillfully use the weather itself for
attacks.

Usopp showed amazing marksmanship and all kinds of new pop
green. Even developed Kenbunshoku Haki.

Ok, everyone is making speculations and theories on Luffy's
powers to come so I thought I would make one, too. With the gear
fourth revealed we all saw how Luffy works out his power ups:

Gear Second: Engine pumping and Rokushiki Speed.

Gear Third: Elbaf's giants.

Gear Fourth: Nightmare Luffy.

Now, if Luffy is to create a new gear it has to follow the same
pattern.

He has to see something that will inspire him

Be able to adapt it to his fighting style with his fruit.

Have time to develop it.

Now the first two are obvious. The reason I mentioned the third
point is because I believe that Luffy must have seen something
already that will inspire his next gear and give him time to
develop it. It is important however to consider what gear set Luffy
is go…

I just happen to look at this image and thought "WHAT!?!? Isn't
it the same?!?!" or something like that.

Well.... My point goes like this...

We have the Bald Gorousei Guy's Katana.

And we have Zoro's Sandai Kitetsu.

They have of course different colour. But the pattern on the
guard and the hilt are almost the same.

If you look closer, although sandai kitetsu has a cross guard,
the other guy's katana has a guard with the same pattern but 3 ends
and not 4 like a cross.

Here is my guess. It is probably another Kitetsu Sword. And
specifically I think it is the Nidai Kitetsu. I think this because
if you consider that the Shodai Kitetsu has the same pattern in the
guard but with 2 ends like a hourglass then the Nidai Kitetsu will
have a similar guard …